Semiconductor device manufacturing method, heat treatment apparatus, and heat treatment method

ABSTRACT

For manufacture of a semiconductor device using a low heat resistant substrate such as a glass substrate, a method of heat treatment for activating an impurity element that is used to dope a semiconductor film and for performing gettering on the semiconductor film in a short period of time without deforming the substrate, is provided. Also provided is a heat treatment apparatus for carrying out the above heat treatment. The heat treatment method of the present invention involves irradiating an object with light emitted from a lamp light source, and is characterized in that the lamp light source emits light for 0.1 to 20 seconds at a time and that light from the lamp light source irradiates the object several times. The method is also characterized in that the irradiated region is subjected to pulsating light from the lamp light source such that the irradiated region holds the temperature to its highest for 0.5 to 5 seconds. The method is also characterized in that the amount of coolant to be supplied is increased or reduced in accordance with blinking of the lamp light source to enhance the effect of the heat treatment on the semiconductor film and to prevent a heat-induced damage to the substrate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor devicemanufacturing method, a heat treatment apparatus, and a heat treatmentmethod using the apparatus. Specifically, the invention relates to aheat treatment method and a heat treatment apparatus for crystallizingan amorphous semiconductor film, for recrystallizing and activating asemiconductor film that has been brought back to an amorphous state byion implantation or ion doping, and for gettering of a metal elementremaining in the semiconductor film. The invention also relates to asemiconductor device manufacturing method using this heat treatmentmethod.

[0003] 2. Description of the Related Art

[0004] Having silicon as its main ingredient, a crystallinesemiconductor film formed at a process temperature of 600° C. or loweris often called low temperature polysilicon. The primal use of thiscrystalline semiconductor film is of as an active layer for forming achannel formation region, a source or drain region and the like in athin film transistor (hereinafter referred to as TFT). The TFT is formedon a glass substrate to manufacture a liquid crystal display device, andtechnologies related thereto are receiving attention most.

[0005] Technologies for manufacturing a TFT using the above crystallinesemiconductor film characteristically employ laser annealing and iondoping, and these techniques make it possible to form an n-channel TFTand a p-channel TFT on a large area glass substrate to build anintegrated circuit having the CMOS structure.

[0006] A TFT needs, in addition to an impurity region of n type or ptype conductivity to serve as a source and drain region, a lowconcentration impurity region that serves as LDD (lightly doped drain)useful in reducing leak current and in stabling TFT characteristics. TheTFT also needs to be doped with an impurity element of one conductivitytype in order to control the threshold voltage. Formation of the lowconcentration impurity region and the doping with an impurity element ofone conductivity type are conducted through ion doping and subsequentactivation treatment. In this ion doping, all of ion species generatedare implanted by acceleration implantation without being subjected tomass separation.

[0007] The impurity is activated after doping by furnace annealing,laser annealing, or RTA (rapid thermal annealing). The source and drainregion, which is relatively heavily doped (concentration: 10¹⁵atoms/cm²), is said to need a rather high temperature and take a longertime to activate the impurity element used in doping for enhancement ofconductance. Laser annealing melts a semiconductor film and isunsatisfactory in controllability and reproducibility, which makes itdifficult to employ laser annealing in a mass production process. On theother hand, furnace annealing is suitable for a mass production processsince it treats in batches but its activation efficiency decreases asthe process temperature becomes low to prolong the treatment time, whichis a problem.

[0008] Laser annealing as a crystallization technique is capable offorming a crystalline semiconductor film on a glass substrate. However,the reaction is of nonequilibrium one and the crystals formed thereforehave small grain size and many defects. Laser annealing crystallizationhas little direct control factors other than the energy density andirradiation number of laser light and the substrate heating temperature.Furthermore, the direct control factors are effective only for limitedranges. For example, control by energy density is effective when it is250 to 400 mJ/cm² and it only gives an amorphous structure outside therange.

[0009] A crystallization technique involving adding with a metal elementis disclosed in Japanese Patent Application Laid-open No. Hei 7-183540as a method that can provide better crystals than those obtained bylaser annealing. The metal element used is nickel, palladium, lead, orthe like. Various methods can be employed in the doping, such as plasmatreatment, evaporation, ion implantation, solution application, andsputtering. Crystallization is made by heat treatment at 500 to 600° C.,preferably 550° C. for four hours. However, this method leaves the metalelement in the semiconductor film crystallized and often needsgettering. Most of the remaining metal element forms a deep level in theforbidden band of the semiconductor film to act as a lifetime killer andto cause an increase of leak current in the junction.

[0010] Gettering using phosphorus can make the metal element segregatein a region doped with phosphorus. This gettering uses an annealingfurnace and requires heat treatment typically at 450 to 600° C. fortwelve hours. The metal element thus segregates in the phosphorus-dopedregion.

[0011] One of the most promising application fields for the thusmanufactured TFT is liquid crystal displays and other flat paneldisplays. In the flat panel display field, increasing the substrate sizeis demanded for improvement of productivity. These larger substratescome in various sizes and 960×1100 mm² is among them. A substratemeasuring 1000 mm or more in one side is more often considered thanothers. Liquid crystal display devices are not the only ones who facethis demand but it is a common object to all large-area integratedcircuits constructed from TFTs formed on glass substrates.

[0012] In order to improve the productivity, it is necessary to reducethe number of steps in a TFT manufacturing process and shorten thetreatment time. Then, a furnace annealing apparatus, which treats inbatches, would not be helpful in improving the production efficiency. Ifthe furnace annealing apparatus is enlarged, current consumption isincreased for heating the large capacity furnace, not to mention itneeds larger installment area.

[0013] RTA is suitable in terms of productivity. RTA is capable ofheating and raising the temperature high in a short period of time andlatently has higher processing ability than furnace annealing also whenthe single wafer method is employed. However, short heating time meanshigh heating temperature while a temperature exceeding the distortionpoint of glass, or even its softening point, is required in order toobtain desired effects in activation and gettering. For instance, aglass substrate is bent and deformed by its own weight by merely sixtyseconds of heat treatment at 800° C. for the purpose of gettering.

SUMMARY OF THE INVENTION

[0014] The present invention has been made to solve the problems above,and an object of the present invention is therefore to provide, formanufacture of a semiconductor device using a low heat resistantsubstrate such as a glass substrate, a method of heat treatment foractivating an impurity element that is used to dope a semiconductor filmand for performing gettering on the semiconductor film in a short periodof time without deforming the substrate. Another object of the presentinvention is to provide a heat treatment apparatus for carrying out theabove heat treatment, and a method of manufacturing a semiconductordevice using the heat treatment apparatus.

[0015] In order to attain the above objects, the present inventionprovides a method of heat treatment for performing gettering andactivation on a semiconductor film formed on a low heat resistantsubstrate such as a glass substrate in a short period of time withoutcausing deformation or other heat-induced damage to the substrate, aswell as a heat treatment apparatus for carrying out the method.

[0016] A semiconductor film is formed on a substrate and then doped withphosphorus by ion doping using phosphine without mass separation.Phosphorus getters a metal element in the semiconductor film through amechanism inferred as follows. When the semiconductor film isselectively doped with phosphorus, a region of the semiconductor filmthat is doped with phosphorus (gettering region) becomes amorphous. Thesemiconductor film is then heated so that the amorphous gettering regionis crystallized. At this point, phosphorus in the gettering region ismoved into a lattice cell of the semiconductor film. The heat treatmentcuts the bond of a compound formed from the metal element (referred toas metal compound) in a region that is not doped with phosphorus(to-be-gettered region) (severing of the bond will be called release).Then, the metal element moves (diffusion) to couple with phosphorus(trapping). The metal element is removed from or reduced in theto-be-gettered region supposedly in this way.

[0017] Gettering is done through three stages: one, release of the metalelement from the metal compound in the to-be-gettered region, two,diffusion of the metal element, and three, trapping of the metal elementby phosphorus in the gettering region. The energy required for releaseof the metal element is estimated as several hundreds degree (° C.) andit is known that the metal element is readily released through heattreatment around 500° C. When the heat treatment is conducted at highertemperature, the rate the metal element diffuses is raised but effectivegettering of the metal element cannot be expected. This is probablybecause phosphorus is stuck in a lattice cell and prevented fromcoupling with the metal element when the temperature is high.

[0018] Accordingly, for effective gettering, the heat treatment has tobe made at low temperature while accelerating diffusion of the metalelement. The invention achieves this by heating the to-be-getteredregion at a temperature higher than the temperature at which thegettering region is heated through pulsative radiation from a lamp lightsource. Structures of the gettering region and the to-be-gettered regionare accordingly modified and a light absorbing film is formed on thegettering region. A gate electrode may serve as the light absorbingfilm. In this case, a part of the gate electrode is formed from, forexample, a tantalum nitride film so that the tantalum nitride film isheated through the radiation from the lamp light source.

[0019] The metal element is readily released from the metal compound anddiffuses into the gettering region by heating the to-be-gettered regionat relatively high temperature. Then, the metal element reaches thegettering region doped with phosphorus and segregates there. Highgettering effect is obtained if the heating is stopped before phosphorusis taken to a lattice cell of the silicon network and forms tetradentatebond, in other words, before activation proceeds too far.

[0020] The treatment object, namely, the semiconductor film, is heatedby irradiating it several times using pulsative radiation from the lamplight source. This makes it possible to rapidly heat and rapidly coolthe to-be-gettered region before heat is transmitted to the glasssubstrate and the gettering region. The light source could be a laser,of course, but a halogen lamp or the like is preferable considering asuitable irradiation time for activation and gettering since irradiatinga large area is easy with a lamp light source. The present invention ischaracterized by conducting gettering and activation in this way.

[0021] As described above, the heat treatment method of the presentinvention involves heating a treatment object by irradiating it severaltimes through pulsative radiation from a lamp light source, and ischaracterized in that radiation from the lamp light source lasts 0.1 to20 seconds at a time and that radiation from the lamp light source isrepeated several times. The method is also characterized in that thetreatment object is subjected to pulsative radiation from the lamp lightsource such that the treatment object holds the temperature to itshighest for 0.5 to 5 seconds. The method is also characterized in thatthe amount of coolant to be supplied is increased or reduced inaccordance with blinking of the lamp light source to enhance the effectof the heat treatment on a semiconductor film that is the treatmentobject and to prevent a heat-induced damage to a substrate.

[0022] A heat treatment apparatus of the present invention is forcarrying out the above heat treatment method and is characterized bycomprising: a lamp light source; a power source for making the lamplight source blink and pulsate; a stage on which a substrate is placed;a processing chamber in which a treatment object is subjected toradiation from the lamp light source; and means for supplying a coolantto the processing chamber and increasing and reducing the amount ofsupply.

[0023] The lamp light source may be a halogen lamp, a metal halide lamp,a xenon lamp, a high pressure mercury lamp, a high pressure sodium lamp,or an excimer lamp.

[0024] The heat treatment apparatus of the present invention may takeanother structure, which is characterized by comprising: a lamp lightsource; a power source for making the lamp light source blink andpulsate; a stage on which a substrate is placed; a processing chamber inwhich a treatment object is subjected to radiation from the lamp lightsource; transferring means for moving the stage in one direction in theprocessing chamber; and means for supplying a coolant to the processingchamber and increasing and reducing the amount of supply in accordancewith blinking of the lamp light source.

[0025] A semiconductor device manufacturing method of the presentinvention employs the above heat treatment method, and is characterizedby comprising the steps of: forming a semiconductor film on a lighttransmissive substrate; forming an insulating film on the semiconductorfilm; forming a light absorptive first conductive film on the insulatingfilm; forming a light reflective second conductive film on the firstconductive film; doping the semiconductor film with an impurity of oneconductivity type to form a semiconductor region of one conductivitytype; and activating the semiconductor region of one conductivity typeby irradiating the region several times from the light transmissivesubstrate side through pulsative radiation from a lamp light source.

[0026] The semiconductor device manufacturing method of the presentinvention may take another structure, which is characterized bycomprising: a first step of forming an amorphous semiconductor film onone major surface of a light transmissive substrate; a second step ofdoping the amorphous semiconductor film with a metal element and thencrystallizing the amorphous semiconductor film to form a crystallinesemiconductor film; a third step of forming, above the crystallinesemiconductor film, a conductive film so as to partially overlap thecrystalline semiconductor film; a fourth step of forming a semiconductorregion doped with phosphorus in the crystalline semiconductor film; anda fifth step of performing intermittent radiation from a lamp lightsource several times from a surface opposite to the one major surface ofthe light transmissive substrate.

[0027] The treatment object is kept in the coolant and is irradiatedseveral times by radiation from the lamp light source such that thetreatment object holds the temperature to its highest, 600 to 800° C.,for 30 to 600 seconds. In this way, the treatment object can be heatedefficiently, completing the heat treatment. The wavelength of theelectromagnetic wave radiated from the lamp light source is matched tothe absorption band of the treatment object for selective heating sothat the treatment object alone is heated. Specifically, a semiconductorfilm formed on a glass substrate having a distortion point of 700° C. orlower is heated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the accompanying drawings:

[0029]FIG. 1 is a diagram illustrating a heat treatment method of thepresent invention;

[0030]FIG. 2 is a diagram showing how a change in amount of coolantsupply is in timing with blinking of a lamp light source;

[0031]FIG. 3 is a graph showing a temperature change in an irradiationobject region due to pulsative radiation from a lamp light source;

[0032]FIG. 4 is a diagram illustrating the mechanism of heat treatmentaccording to the present invention;

[0033]FIG. 5 is a diagram illustrating the structure of a heat treatmentapparatus according to the present invention;

[0034]FIGS. 6A to 6C are diagrams illustrating a heat treatment methodof the present invention;

[0035]FIGS. 7A to 7F are sectional views illustrating a method ofmanufacturing TFTS;

[0036]FIGS. 8A to 8C are sectional views illustrating a method offorming a semiconductor film;

[0037]FIG. 9 is a diagram illustrating a gettering method;

[0038]FIGS. 10A to 10C are sectional views illustrating a process ofmanufacturing a semiconductor device provided with a driving circuitportion and a pixel portion;

[0039]FIGS. 11A to 11C are sectional views illustrating a process ofmanufacturing a semiconductor device provided with a driving circuitportion and a pixel portion;

[0040]FIGS. 12A and 12B are sectional views illustrating a process ofmanufacturing a semiconductor device provided with a driving circuitportion and a pixel portion;

[0041]FIG. 13 is a top view illustrating the structure of a pixelportion;

[0042]FIG. 14 is a diagram illustrating the structure of a liquidcrystal display device obtained by the present invention;

[0043]FIG. 15 is a diagram illustrating the structure of a lightemitting device obtained by the present invention;

[0044]FIG. 16 is a diagram illustrating the structure of a heattreatment apparatus according to the present invention;

[0045]FIGS. 17A to 17C are micrographs of semiconductor films afterreceiving activation treatment in accordance with a heat treatmentmethod of the present invention;

[0046]FIGS. 18A to 18E are diagrams showing examples of a semiconductordevice;

[0047]FIGS. 19A to 19C are diagrams showing examples of a semiconductordevice;

[0048]FIGS. 20A to 20D are diagrams illustrating the structure ofprojectors;

[0049]FIGS. 21A and 21B are a top view of a pixel portion and asectional view thereof, respectively; and

[0050]FIG. 22 is an ogive graph showing the distribution of OFF currentof TFTs in plural samples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIEMNTS

[0051] An embodiment mode of the present invention will be described indetail below with reference to the accompanying drawings. Referring toFIG. 1, a description is given on the concept of a heat treatmentapparatus according to the present invention. FIG. 1 is a diagramshowing the structure of the heat treatment apparatus according to thepresent invention. A processing chamber 101 is preferably formed ofquartz and has a lamp light source 102 as means for heating a treatmentobject 106. The lamp light source 102 is placed outside the processingchamber 101, and is provided with a reflective plate 103 so that asubstrate 106 is efficiently irradiated with the radiated heat. Acoolant inlet 104 is provided to cool the substrate 106, and a coolantis introduced to the chamber when the substrate is heated. A coolant 105may be inert gas such as nitrogen and helium, or a liquid. Desirably,the coolant has high purity. Whatever material is used, the coolant isdesirably a medium that absorbs little heat radiated from the lamp lightsource 102.

[0052] The lamp light source is lit and made to pulsate by its powersource and a control circuit. FIG. 2 shows how the treatment objectheated by the lamp light source and the amount of coolant supplied tothe processing chamber are controlled. First, the treatment object,which has been kept at room temperature, is rapidly heated by the lamplight source. The temperature of the treatment object is raised at arate of 100 to 200° C. per second until a set temperature (1100° C., forexample) is reached. If the treatment object is heated at a temperaturerise rate of 150° C. per second, for instance, it reaches 1100° C. inless than 7 seconds. The set temperature is kept for a given period oftime while the lamp light source stops emit light. The given period oftime ranges from 0.5 to 5 seconds. Accordingly, the lamp light sourceemit light continuously for equal to and longer than 0.1 second andshorter than 20 seconds. The amount of coolant supplied is reduced asthe lamp light source starts to emit light and increased as the lamplight source stops emitting light. By controlling the amount of coolantsupply, how fast the heat treatment object looses temperature iscontrolled. The temperature drop rate is set to 50 to 150° C. persecond. For example, when the treatment object is cooled at a rate of100° C. per second, the temperature thereof drops from 1100° C. to 300°C. in 8 seconds.

[0053] The present invention is characterized by repeating the cycle ofheating and cooling several times. The actual heating time is shortenedand the lamp light source irradiates a semiconductor film with lightthat is selectively absorbed by the semiconductor film, so that thesemiconductor film alone is selectively heated without giving thesubstrate too much heat. The pulsative radiation as shown in FIG. 2heats the semiconductor film and then stops heating before the heat istransmitted to the substrate. Simultaneously, the substrate is cooled bythe surrounding coolant and therefore the temperature of the substrateis not raised much. Deformation of the substrate, which has been theproblem of any conventional RTA apparatus, thus can be prevented.

[0054] As shown in FIG. 4, the treatment object is a light transmissivesubstrate 201 such as a glass substrate, on which a semiconductor film203 is formed. On the semiconductor film 203, a conductive layer isformed. The conductive layer may be a single layer but, preferably,consists of a light absorptive first conductive film 205 and a heatconductive second conductive film 206. A first insulating film 202 and asecond insulating film 204 are formed on the substrate side and theopposite side of the semiconductor film 203, respectively.

[0055] The pulsative radiation from the lamp light source irradiates thesemiconductor film from the substrate 201 side. As shown in FIG. 2, thepulsative radiation pulsates for intermittent irradiation. The spacesurrounding the substrate is filled with a coolant 207 such as nitrogengas. Due to this pulsative radiation, the temperature of the treatmentobject is different between a region A and a region B as shown in thegraph in FIG. 4.

[0056] The pulsative radiation is partially absorbed by thesemiconductor film 203 and is converted into heat except the part thatis reflected at various interfaces. Light that reaches the lightabsorptive first conductive film 205 in the region B is absorbed in theregion and converted into heat. Some of the heat generated there istransmitted to the semiconductor film 203 through the second insulatingfilm 204. On the other hand, light that has entered the region A istransmitted to the space filled with the coolant 207 through the secondinsulating film 204. Accordingly, the temperature rises differentlybetween the region A and the region B when the regions receive thepulsative radiation of the same intensity repeatedly. This creates atemperature gradient in the semiconductor film in the direction parallelto the substrate surface (referred to as the horizontal direction forconveniences' sake).

[0057] This temperature gradient can be utilized effectively whengettering a channel formation region with the region B as the channelformation region and the region A as an impurity semiconductor region.To be specific, the region A is doped with phosphorus to form an n typesemiconductor region and then the region B is gettered and a metalelement contained in the region B segregates in the region A byrepeating pulsative radiation as shown in FIG. 2.

[0058] This gettering effect can be adopted particularly when asemiconductor film is added with a metal element for crystallization andthe metal element is to be removed later from a channel formation regionthereof.

[0059] Because of the conductive film covering the semiconductor film,the temperature of the region of the semiconductor film that is coveredwith the conductive film (the region B in FIG. 4) is higher than that ofthe other region of the semiconductor film (the region A in FIG. 4). Theconfiguration shown in FIG. 4 can be translated into a glass substrateon which a semiconductor film, a gate insulating film (corresponding tothe second insulating film 204), and a gate electrode (corresponding tothe first conductive film 205 and the second conductive film 206) areformed. Then, this configuration may not provide uniform heat treatmenteffect when applied to a device in which a pixel portion is formed onthe same substrate as a driving circuit portion to be provided in theperiphery of the pixel portion, as in a liquid crystal display device.The pixel portion and the driving circuit portion are different fromeach other in TFT density, and TFTs are formed in the driving circuitportion at far greater density than in the pixel portion. Therefore thetemperature in the driving circuit portion is raised higher when boththe pixel portion and the driving circuit portion receive the pulsativeradiation of the same intensity repeatedly.

[0060] In order to obtain uniform heat treatment effect, light intensityis partially attenuated on the incident side of the pulsative radiationfrom the lamp light source, as shown in FIGS. 6A to 6C. FIG. 6A shows anexample of how to attenuate the pulsative radiation. In FIG. 6A, a pixelportion 402 and a driving circuit portion 403 are formed on a lighttransmissive substrate 401. On one side of the substrate 401 wherepulsative radiation 406 enters the substrate, a semi-transmissive film405 that is a metal thin film formed of chromium or the like is placedin an area corresponding to the driving circuit portion 403. Then, thepulsative radiation is attenuated. FIG. 6B shows another example ofattenuating the pulsative radiation, in which the semi-transmissive filmis replaced by a slit portion 407. FIG. 6C shows still another examplein which a metal mask 408 has an opening 410 in an area corresponding tothe pixel portion and has a slit portion 409 in an area corresponding tothe driving circuit portion. The degree of attenuation of the pulsativeradiation is set suitably, and is readily adjusted by adjusting thetransmittance of the semi-transmissive film or the aperture ratio of theslit portion.

[0061] As described above, the present invention provides a method ofheat treatment that can activate an impurity element used to dope asemiconductor film and perform gettering on the semiconductor film in ashort period of time without deforming a substrate even if it is a lowheat resistant substrate such as a glass substrate. This heat treatmentcan be incorporated in a process of manufacturing a semiconductordevice.

[0062] Embodiment 1

[0063]FIG. 5 shows the structure of a single wafer type heat treatmentapparatus as an example of a heat treatment apparatus of the presentinvention. A processing chamber 301 is formed of quartz and issurrounded by water-cool type cooling means 305. A lamp light source 302has a reflective plate 303 so that pulsative radiation diffuses over atreatment object 317 efficiently. When a rod-like halogen lamp is used,a plurality of lamps are set as shown in FIG. 5 to irradiate thetreatment object 317 with pulsative radiation of uniform intensity.Radiation (including a wavelength of 0.5 μm to 3 μm, for example) ismade to pulsate by a light source control unit 304.

[0064] Nitrogen gas is supplied as a coolant to the processing chamber301 from a coolant supply source 306. The amount of nitrogen gas to besupplied to the processing chamber 301 can be controlled by flow ratecontrolling means 307. The coolant supplied to the processing chamber isthen discharged from an outlet 311 so that the processing chamber isalways filled with clean nitrogen gas. A temperature detector 309 iscomprised of a temperature sensor 308 that is a radiation thermometerand is provided to monitor the temperature of the treatment object thatis heated by pulsative radiation from the lamp light source. For thatreason, the temperature sensor 308 is placed on a part of a stage 318.

[0065] Control means 310 controls the operation of the light sourcecontrolling unit 304 and the flow rate controlling means 307 such thatblinking of the lamp light source is synchronized with increase orreduction of the amount of coolant supply as shown in FIG. 2. Thecontrol means 310 also receives a signal from the temperature detector309 to detect the temperature of the treatment object and determinewhether there is a trouble or not.

[0066] The treatment object is set in a substrate holder 316 in aloading/unloading chamber 315, and then transferred to the processingchamber 301 by transferring means 314 of a transfer chamber 313. A gatevalve 312 is provided between the transfer chamber 313 and theprocessing chamber 301 to allow the coolant to fill the processingchamber 301 during heat treatment.

[0067] An impurity element used to dope a semiconductor film isactivated by the following procedure. The semiconductor film is formedon one major surface of a glass substrate. The treatment object havingthe semiconductor film is set in the loading/unloading chamber 315, andthen taken out of the substrate holder 316 by the transferring means 314of the transfer chamber 313 to be set on the stage 318 of the processingchamber 301. The treatment object is set on the stage such that thesemiconductor film faces the opposite side of the lamp light source 302.In other words, the semiconductor film receives radiation through theglass substrate.

[0068] Thereafter, the gate valve 312 is closed. The flow ratecontrolling means 307 keeps supplying the processing chamber that has avolume of 18×30×1.5 cm³ with the coolant at a flow rate of 1 to 2 litersper minute. After the gate valve 312 is closed, the flow ratecontrolling means increases the amount of coolant supply to 10 to 20liters per minute and holds the rate for a given period of time, so thatthe atmosphere of the processing chamber is substituted with thecoolant, i.e., nitrogen gas.

[0069] As the lamp light source starts to emit light, the amount ofnitrogen gas supplied is reduced to 2 liters per minute. The treatmentobject is heated by the lamp light source at a rate of 100 to 200° C.per second until it reaches 1100° C. based on the temperature detectedby the temperature sensor 308. Then, heating is controlled so that thetreatment object is kept at 1100° C. for 0.5 to 5 seconds. The lamplight source is then turned off and the flow rate of nitrogen gas israised to 10 liters per minute to cool the treatment object down to 300to 400° C. at a rate of 50 to 150° C. per second. This state may last 5to 60 seconds (corresponding to a holding period (2) in FIG. 2). FIG. 3is a graph obtained by plotting a change with time in temperaturedetected by the temperature sensor. Shown in FIG. 3 is data of when thetreatment object is kept at 1100° for 4.2 seconds and data of when it iskept for 0.75 seconds. Table 1 and Table 2 contain numerical data forthe graph of FIG. 3 and show the temperature measured at various timepoints and the rate of temperature change. TABLE 1 Time [s] Temp. [° C.]Rate of Temp. Change [° C./s] Heating 10.25 93.30 115.60 Process 11.00180.00 161.29 11.62 280.00 140.39 12.38 386.70 173.20 12.88 473.30187.40 13.38 567.00 159.40 13.88 646.70 288.11 14.25 753.30 201.11 14.88880.00 144.19 15.62 986.70 106.60 Holding 16.62 1093.30 9.71 Process18.00 1106.70 −6.32 20.12 1093.30 −66.67 Cooling 21.62 993.30 −128.75Process 22.50 880.00 −113.64 23.38 780.00 −63.28 24.75 693.30 −53.4826.62 593.30 −30.67 29.88 493.30 −17.79 35.50 393.30 −8.99 46.62 293.30

[0070] TABLE 2 Time [s] Temp. [° C.] Rate of Temp. Change [° C./s]Heating 17.00 580.00 173.40 Process 17.50 666.70 200.00 18.00 766.70253.20 18.50 893.30 93.40 19.50 986.70 106.60 20.50 1093.30 26.80Holding 20.75 1100.00 0.00 Process 21.00 1100.00 −80.00 Cooling 21.251080.00 −142.27 Process 22.00 973.30 −106.67 22.75 893.30 −133.33 23.50793.30 −66.67 25.00 693.30 −60.91 26.75 586.70 21.93

[0071] Bending of the substrate can be avoided by irradiating thesubstrate several times through pulsative radiation described above.This applies to the case of activating an impurity element used to dopea semiconductor film and the case of gettering the semiconductor filmboth.

[0072] Embodiment 2

[0073] As an example of a heat treatment apparatus of the presentinvention, the structure of an inline type heat treatment apparatus thatcorresponds to a substrate having a large area is shown in FIG. 16. Aprocessing chamber 1301 is formed of quartz and is surrounded bywater-cool type cooling means 1305. A lamp light source 1302 has areflective plate so that an optical lens 1324 condenses light toirradiate a treatment object. A rod-like halogen lamp is used in a lamplight source 1302, and a cylindrical lens is used as the optical lens1324, thereby being capable of irradiating the treatment object with alinear light. A lamp light source is lit and made to pulsate by a lightsource control unit 1304.

[0074] Nitrogen gas or helium gas is supplied as a coolant to theprocessing chamber 1301 from a coolant supply source 1306. The amount ofnitrogen as to be supplied to the processing chamber 1301 can becontrolled by a flow rate controlling means 1307. The coolant suppliedto the processing chamber is then discharged outside from an outlet 1311so that the processing chamber is always filled with clean nitrogen gas.

[0075] Control means 1310 controls the operation of the light sourcecontrolling unit 1304, the flow rate controlling means 1307 and atransferring means 1323 of a treatment object 1317 and a stage 1318 inthe processing chamber, such that blinking of the lamp light source issynchronized with increase or reduction of the supply amount of coolant,as shown in FIG. 2. The control means 1310 also controls the timing inwhich the stage 1318 moves.

[0076] The treatment object is put on the stage and is set in a holder1316 in a loading chamber 1315, and then transferred to the processingchamber 1301 by a transferring means 1314 of a transfer chamber 1313. Agate valve 1312 is provided between the transfer chamber 1313 and theprocessing chamber 1301 to allow the coolant to fill the processingchamber 1301 during heat treatment.

[0077] A treatment object 1317 is irradiated with pulsative radiationfrom the lamp light source 1302 while placed on the stage 1318 and movedby the transferring means 1323 of the processing chamber 1301. Theentire surface of the treatment object thus receives heat treatment.After finishing the heat treatment, the treatment object 1317 is movedto a transfer chamber 1320 along with the stage 1318 by transferringmeans 1321. Thereafter, the treatment object is received by a holder1326 in an unloading chamber 1322.

[0078] The treatment object is heated in a manner similar to thetreatment in Embodiment 1. However, since the treatment object is movedalong in the apparatus structured as shown in FIG. 16, the movement hasto be in timing with the pulsative radiation. The flow rate of nitrogengas used as the coolant is controlled similarly. The treatment object ismoved during the holding period (2) shown in FIG. 2, and it is a phasedprogress. How far the treatment object moves at a time can be setsuitably, but the movement has to be one that allows the pulsativeradiation to irradiate the same region several times.

[0079] With this structure, the size of apparatus does not need to bevery large to perform heat treatment on a large-area substrate. Bendingof the substrate can be avoided and the gettering can be performed byirradiating the substrate several times through pulsative radiationdescribed above. This applies to the case of activating an impurityelement used to dope a semiconductor film and the case of gettering thesemiconductor film both.

[0080] Embodiment 3

[0081] An example of a method of manufacturing TFTs using the presentinvention will be described with reference to FIGS. 7A to 7F. In FIG.7A, a crystalline semiconductor film mainly containing silicon is formedon a light transmissive substrate 501 formed of alminoborosilicate glassor barium borosilicate glass. The crystalline semiconductor film isobtained by crystallizing an amorphous semiconductor film through laserannealing. Instead, the heat treatment apparatus described in Embodiment1 or Embodiment 2 may be used to crystallize an amorphous semiconductorfilm through pulsative radiation. The crystalline semiconductor filmformed has a thickness of 25 to 80 nm. To manufacture TFTs, thecrystalline semiconductor film is etched and divided into films havinggiven sizes for element separation. Thus formed are island-likesemiconductor films 503 to 505. A first insulating film 502 with athickness of 50 to 200 nm is formed between the substrate 501 and thesemiconductor films. The first insulating film is formed of one selectedfrom the group consisting of silicon nitride, silicon oxide, and siliconoxynitride, or a combination thereof.

[0082] For example, the first insulating film 502 may be a siliconoxynitride film formed by plasma CVD from SiH₄ and N₂O to have athickness of 50 to 200 nm. The first insulating film 502 may also take atwo-layer structure consisting of a silicon oxynitride film that isformed by plasma CVD from SiH₄, NH₃, and N₂O to have a thickness of 50nm and a silicon oxynitride film that is formed by plasma CVD from SiH₄and N₂O to have a thickness of 100 nm. Another example of the two-layerstructure for the first insulating film consists of a silicon nitridefilm and a silicon oxide film that is formed from TEOS (tetraethyl orthosilicate).

[0083] On the semiconductor films 503 to 505, a silicon oxide film 506is formed by plasma CVD to have a thickness of 100 nm. A mask 507 isformed thereon from a resist to dope the semiconductor film 504 with ann type impurity element (donor). As a result, a first n typesemiconductor region 508 is formed in the semiconductor film 504 asshown in FIG. 7A. The n type impurity (donor) typically used isphosphorus, and the phosphorus concentration in the first n typesemiconductor region 508 is 1×10¹⁷ to 1×10¹⁹ atoms/cm³ on the average.The silicon oxide film 506 is used here as a mask for controlling thephosphorus concentration.

[0084] Accordingly, the silicon oxide film 506 is removed using fluoricacid and the like after the doping. A second insulating film 509 is thenformed to have a thickness of 80 nm. The second insulating film 509 isused as a gate insulating film and formed by plasma CVD or sputtering.If the second insulating film 509 is a silicon oxynitride film formed byadding O₂ to SiH₄ and N₂O, it makes a preferable gate insulating filmsince the fixed electric charge density in the film is low. Needless tosay, the gate insulating film is not limited to the silicon oxynitridefilm as this and may be a single layer or a laminate of insulating filmssuch as a silicon oxide film and a tantalum oxide film.

[0085] On the second insulating film 509, a first conductive film and asecond conductive film constituting gate electrodes are formed. Thefirst conductive film is a light absorptive conductive film. An exampleof such conductive film is a tantalum nitride film, and one having athickness of 50 to 100 nm is used here. The second conductive film isformed of a high melting point metal such as tungsten and molybdenum andhas a thickness of 100 to 300 nm. These materials are stable and theirresistivity does not increase much during heat treatment at 400 to 600°C. in a nitrogen atmosphere.

[0086] Next, the first conductive film and the second conductive filmare etched to form gate electrodes 510 to 512 (the gate electrode 510 iscomposed of a first conductive film 510 a and a second conductive film510 b, the gate electrode 511 is formed of a first conductive film 511 aand a second conductive film 511 b, and the gate electrode 512 is formedof a first conductive film 512 a and a second conductive film 512 b) asshown in FIG. 7B. The etching method is not particularly limited but,preferably, ICP (inductively coupled plasma) etching is employed. Amixture gas of CF₄ and Cl₂ is used as the etching gas in this etching.

[0087] After the gate electrodes are formed, the semiconductor films 503to 505 are doped with an n type impurity (donor) by ion doping whileusing the gate electrodes as masks. Thus formed are second n typesemiconductor regions 513 to 515. The phosphorus concentration in thesecond n type semiconductor regions 513 to 515 is 1×10¹⁶ to 1×10¹⁸atoms/cm³ on the average. However, the second n type semiconductorregions have to be doped with the impurity in a concentration lower thanthe impurity concentration in the first n type semiconductor region.Therefore, the first n type semiconductor region formed in thesemiconductor film 504 remains as it is.

[0088] Subsequently, masks 516 and 517 are formed from a resist on thesemiconductor films 503 and 505 as shown in FIG. 7C. Then, thesemiconductor films are again doped with the n type impurity (donor) byion doping, thereby forming third n type semiconductor regions 518 to520. The phosphorus concentration in the third n type semiconductorregions is 1×10²⁰ to 1×10²¹ atoms/cm³ on the average. At this point, apart of the first n type semiconductor region 508 in the semiconductorfilm 504 is remained in a region overlapping the gate electrode. A partof the second n type semiconductor region 515 in the semiconductor film505 is remained in a region overlapping the mask 517.

[0089] As shown in FIG. 7D, a mask 521 is then formed from a resist todope the semiconductor film 503 for forming a p-channel TFT with a ptype impurity (acceptor). The p type impurity typically used is boron(B). Thus formed is a first p type semiconductor region 522, which hasan impurity concentration of 2×10²⁰ to 2×10²¹ atoms/cm³. Theconcentration of boron used here is 1.5 to 3 times the concentration ofphosphorus that has already been contained in this region, so that theconductivity of the region is inverted from n type to p type.

[0090] In FIG. 7E, the impurities used in doping are activated by heattreatment. The heat treatment is carried out by using the heat treatmentapparatus described in Embodiment 1 or Embodiment 2, and the impuritiesare activated by irradiating the semiconductor films several timesthrough pulsative radiation. Since the irradiation is performed from thesubstrate side, the p type and n type impurity elements can be activatedwithout fail throughout the entire semiconductor films, even in thefirst n type semiconductor region that overlaps the gate electrode.

[0091] Through the above steps, doping of the semiconductor films withimpurities to form source or drain regions and LDD regions in therespective semiconductor films is completed, as well as activation ofthe impurities. Thereafter, a protective insulating film 526 is formedfrom a silicon nitride film or a silicon oxynitride film by plasma CVDas shown in FIG. 7F. Heat treatment is then conducted at 350 to 450° C.,preferably, 410° C. Hydrogen in a first interlayer insulating film isreleased at this temperature and the semiconductor film is hydrogenated.Therefore, heat treatment using a furnace annealing or a clean oven ismore suitable for this purpose.

[0092] An interlayer insulating film 527 is formed from an organicinsulating material such as polyimide and acrylic to level the surface.A silicon oxide film formed by plasma CVD from TEOS (tetraethyl orthosilicate) may of course be used instead, but the organic resin materialis preferable for superior flatness.

[0093] Next, contact holes are formed and source or drain wiring lines528 to 533 are formed from aluminum (Al), titanium (Ti), tantalum (Ta),or the like.

[0094] A p-channel TFT 540 manufactured through the above steps has achannel formation region 523 and the first p type semiconductor region522 that functions as a source or drain region. An n-channel TFT 541 hasa channel formation region 524, the first n type semiconductor region508 that overlaps the gate electrode 511, and the third n typesemiconductor region 519 that functions as a source or drain region. Thefirst n type semiconductor region is an LDD region which, whenoverlapping a gate electrode, can ease the high electric field regiongenerated in an end of the drain and prevent degradation of the TFT dueto the hot carrier effect. An n-channel TFT 542 has a channel formationregion 525, the second n type semiconductor region 515 that is formedoutside the gate electrode 512, and the third n type semiconductorregion 520 that functions as a source or drain region. The second n typesemiconductor region 515 is an LDD region and can reduce OFF current ofthe TFT. The manufacture process shown in this embodiment allows thedimensions to be set to values optimal for reducing the OFF currentvalue.

[0095] Thus obtained is a CMOS TFT in which an n-channel TFT and ap-channel TFT are combined complementarily. The manufacture processshown in this embodiment allows an operator to design LDD regions takinginto consideration characteristics required for the respective TFTs, sothat TFTs on the same substrate can have individually optimalstructures. This CMOS TFT can make a driving circuit of an activematrix-driven display device. The n-channel TFT or the p-channel TFT ofthis CMOS TFT is adaptable as a transistor constituting a pixel portion.It can be used also as a TFT for making a thin film integrated circuitthat is to replace LSI fabricated from a conventional semiconductorsubstrate. The TFTs shown here has a single gate structure but may ofcourse take a multi-gate structure in which a plurality of gateelectrodes are provided.

[0096] In this manufacture process for TFTs, the heat treatmentapparatus of the present invention can be used to conduct activation.Activation by the heat treatment method of the present invention takesonly a short period of time and does not damage a substrate.

[0097] Embodiment 4

[0098] This embodiment describes, as an example of a semiconductordevice manufacturing method using a heat treatment apparatus of thepresent invention, a method of forming a driving circuit and a pixelportion on the same substrate. The driving circuit is composed of ann-channel TFT and a p-channel TFT, and the description will be givenwith reference to FIGS. 10A to 12B.

[0099] Formed first on a substrate 601 as shown in FIG. 10A is a firstinsulating film 602. The first insulating film 602 has a two-layerstructure consisting of a silicon oxynitride film that is formed byplasma CVD from SiH₄, NH₃, and N₂O to have a thickness of 50 nm and asilicon oxynitride film that is formed by plasma CVD from SiH₄ and N₂Oto have a thickness of 100 nm. A substrate appropriate to use here is analuminoborosilicate glass, barium borosilicate glass, or othernon-alkaline glass substrate. The thickness of the substrate is about0.5 to 1.1 mm.

[0100] Semiconductor films 603 to 606 are formed thereon to have athickness of 40 nm. The semiconductor films are polycrystalline siliconobtained by crystallizing, through laser annealing or a solid phasegrowth method, amorphous silicon that is deposited by plasma CVD or lowpressure CVD. Alternatively, the heat treatment apparatus described inEmbodiment 1 or Embodiment 2 may be used to crystallize the amorphoussilicon through pulsative radiation. After subjected to light exposure,the semiconductor films are divided into island-like semiconductorfilms. Hereinafter, the description of this embodiment is given on thepremise that the semiconductor film 603 is used to form a p-channel TFTand the semiconductor films 604 and 605 are used to form n-channel TFTs.The semiconductor film 606 is used to form an auxiliary capacitor.

[0101] A second insulating film 607 with a thickness of 75 nm is formedso as to cover the semiconductor films. The second insulating filmserves as a gate insulating film. Silicon oxide made from TEOS(tetraethyl ortho silicate) or silicon oxynitride made from SiH₄ and N₂Ois used to form the second insulating film and plasma CVD is employedfor the formation.

[0102] Next, a first conductive film 608 and a second conductive film609 are formed on the second insulating film as shown in FIG. 10B. Thefirst conductive film 608 is formed of tantalum nitride whereas thesecond conductive film 609 is formed of tungsten. The conductive filmsconstitute gate electrodes. The first conductive film is 30 nm thick andthe second conductive film is 300 nm thick.

[0103] Thereafter, a resist pattern 610 for forming the gate electrodesand data lines is formed through light exposure as shown in FIG. 10C.The resist pattern is used in first etching treatment. The etchingmethod is not particularly limited but, preferably, ICP (inductivelycoupled plasma) etching is employed. While using CF₄ and Cl₂ as etchinggas for tungsten and tantalum nitride, an RF (13.56 MHz) power of 500 Wis given to a coiled electrode at a pressure of 0.5 to 2 Pa, preferably1 Pa, to generate plasma. At this point, the substrate side (stage) alsoreceives an RF (13.56 MHz) power of 100 W so that substantially negativeself-bias voltage is applied. When a mixture of CF₄ and Cl₂ is used asthe etching gas, tungsten and tantalum nitride are etched at almost thesame rate.

[0104] Under the above etching conditions, the conductive films aretapered around the edges owing to the shape of the resist mask and theeffect of the bias voltage applied to the substrate side. The angle ofthe tapered portion is set to 15 to 45°. In order to etch the conductivefilms without leaving any residue on the gate insulating film, theetching time is prolonged by about 10 to 20%. Since the selective ratioof a silicon oxynitride film to a W film is 2 to 4 (typically, 3), thesurface where the second insulating film is exposed is etched by about20 to 40 nm through the over-etching treatment. Thus formed through thefirst etching treatment are first shape electrodes 611 to 614 (the firstshape electrode 611 is composed of a tantalum nitride film 611 a and atungsten film 611 b, 612 is composed of a tantalum nitride film 612 aand a tungsten film 612 b, 613 is composed of a tantalum nitride film613 a and a tungsten film 613 b, and 614 is composed of a tantalumnitride film 614 a and a tungsten film 614 b,) and a first shape wiringline 615 (composed of a tantalum nitride film 615 a and a tungsten film615 b).

[0105] Then, first doping treatment is conducted to dope thesemiconductor films with an n type impurity (donor). Ion doping or ionimplantation is used. When ion doping is chosen, the dose is set to1×10¹³ to 5×10¹⁴ atoms/cm². An impurity element that imparts the n typeconductivity is a Group 15 element, typically phosphorus (P) or arsenic(As). In the first doping, the first shape electrodes 611 to 614 serveas masks against the dopant. The acceleration voltage is adjustedsuitably (to 20 to 60 keV, for example) so that the semiconductor filmsare doped with the impurity element passing through the secondinsulating film. As a result, first impurity regions 616 to 619 areformed. The phosphorus (P) concentration in the first impurity regions616 to 619 is 1×10²⁰ to 1×10²¹ atoms/cm³.

[0106] Subsequently, second etching treatment is conducted as shown inFIG. 11A. In the second etching treatment, ICP etching is employed, CF₄,CL₂, and O₂ are mixed as etching gas, and an RF (13.56 MHz) power of 500W is given to a coiled electrode at a pressure of 1 Pa to generateplasma. The substrate side (stage) receives an RF (13.56 MHz) power of50 W to apply a self-bias voltage lower than that in the first etchingtreatment. Under these conditions, the tungsten film is subjected toanisotropic etching to leave the tantalum nitride film that is the firstconductive film. Formed through the second etching treatment are secondshape electrodes 620 to 623 (the second shape electrode 620 is composedof a tantalum nitride film 620 a and a tungsten film 620 b, 621 iscomposed of a tantalum nitride film 621 a and a tungsten film 621 b, 622is composed of a tantalum nitride film 622 a and a tungsten film 622 b,and 623 is composed of a tantalum nitride film 623 a and a tungsten film623 b) and a second shape wiring line 624 (composed of a tantalumnitride film 624 a and a tungsten film 624 b). Portions of the secondinsulating film that are not covered with the tantalum nitride films areetched and thinned by about 10 to 30 nm through the second etchingtreatment.

[0107] In second doping treatment, the dose is smaller than that in thefirst doping treatment and the acceleration voltage is set high to dopethe semiconductor films with an n type impurity (donor). For instance,the acceleration voltage is set to 70 to 120 keV and the dose is set to1×10¹³ atoms/cm². As a result, second impurity regions are formed insidethe first impurity regions. The semiconductor films under the exposedtantalum nitride films 620 a to 623 a are doped with the impurityelement that has passed through the films 620 a to 623 a. The secondimpurity regions, denoted by 625 to 628, thus overlap the tantalumnitride films 620 a to 623 a. Although the impurity concentration in thesecond impurity regions fluctuates in accordance with the thicknesschange, the peak concentration is 1×10¹⁷ to 1×10¹⁹ atoms/cm³. The n typeimpurity depth distribution is not uniform in the second impurityregions.

[0108] As shown in FIG. 11B, a resist mask 629 is formed next throughlight exposure so as to cover the second shape gate electrode 621, andthe tantalum nitride films of the other exposed second shape electrodesare selectively etched. A mixture of Cl₂ and SF₆ is used as the etchinggas. Formed as a result are third shape electrodes 630 to 632 in whichthe ends of the tungsten films coincide with the ends of the tantalumnitride films. The data line may simultaneously be processed to form athird shape wiring line 633.

[0109] Then, masks 634 and 635 are formed from a resist as shown in FIG.11C to dope the semiconductor films 603 and 606 with a p type impurity(acceptor). The p type impurity is typically boron (B). Thus formed isfirst p type semiconductor regions 636 and 637, which have an impurityconcentration of 2×10²⁰ to 2×10²¹ atoms/cm³. The concentration of boronused here is 1.5 to 3 times the concentration of phosphorus that hasalready been contained in the regions, so that the conductivity of theregions is inverted from n type to p type.

[0110] Through the above steps, the impurity regions are formed in therespective semiconductor films. The second shape electrode 621 and thethird shape electrodes 630 to 632 serve as gate electrodes. The thirdshape wiring line 633 makes a data line. The gate electrode 632 is oneof electrodes that constitute an added capacitor, and overlaps thesemiconductor film 606 to form the capacitor in the overlapping portion.

[0111] Thereafter, a protective insulating film 638 is formed from asilicon oxynitride film by plasma CVD to have a thickness of 50 nm asshown in FIG. 12A. Then, the impurities used in doping are activatedthrough heat treatment. The heat treatment is carried out by using theheat treatment apparatus described in Embodiment 1 or Embodiment 2, andthe impurities are activated by irradiating the semiconductor filmsseveral times through pulsative radiation. Since the irradiation is madefrom the substrate side, the p type and n type impurity elements can beactivated without fail throughout the entire semiconductor films, evenin the first n type semiconductor regions that overlap the gateelectrode.

[0112] Hydrogenation treatment is necessary to improve the TFTcharacteristics, and is carried out by heat treatment or plasmatreatment in a hydrogen atmosphere. There is another hydrogenationmethod, which is shown in FIG. 12B. In this method, a silicon nitridefilm 640 is formed to have a thickness of 50 to 100 nm and thensubjected to heat treatment at 350 to 500° C. Hydrogen is thus releasedfrom the silicon nitride film 640 and diffuses to the semiconductorfilms to hydrogenate them and repair defects.

[0113] An interlayer insulating film 641 is formed from an organicinsulating material such as polyimide and acrylic to level the surface.A silicon oxide film formed by plasma CVD from TEOS (tefraethyl orthosilicate) may of course be used instead, but the organic material ispreferable for superior flatness.

[0114] Formed next are contact holes starting from the surface of theinterlayer insulating film 641 and reaching the second n typesemiconductor regions or the first p type semiconductor regions of therespective semiconductor films. Then, wiring lines are formed from Al,Ti, Ta, or the like. In FIG. 12B, 642 and 645 denote source wiring lineswhereas 643 and 644 denote drain wiring lines. Denoted by 647 is a pixelelectrode and 646 is a connector electrode that connects the data line633 with a second n type semiconductor region 667 of the semiconductorfilm 605. 648 is a gate wiring line and, though not shown in thedrawing, is connected to the third shape electrode 631 functioning as agate electrode.

[0115] In this way, the TFTs constituting a driving circuit 650 and apixel portion 651 are formed on the same substrate. The driving circuit650 shown in FIG. 12B has a p-channel TFT 652 and an n-channel TFT 653,which can constitute various kinds of functional circuits such as ashift register, a level shifter, a latch, and a buffer circuit. The B-B′sectional view in FIG. 12B corresponds to a view taken along the lineB-B′ in FIG. 13 that shows the pixel structure.

[0116] The p-channel TFT 652 of the driving circuit 650 has a channelformation region 660 and the first p type semiconductor region 661 thatfunctions as a source or drain region. The n-channel TFT 653 of thedriving circuit has a channel formation region 662, a first n typesemiconductor region 663 that overlaps the gate electrode 621, and asecond n type semiconductor region 664 that functions as a source ordrain region.

[0117] An n-channel TFT 654 of the pixel portion 651 has a channelformation region 665, a first n type semiconductor region 666 that isformed outside a gate electrode 640, and second n type semiconductorregions 667 to 669 that function as source or drain regions. Anauxiliary capacitor 655 is composed of the semiconductor film 606, thesecond insulating film 607, and the gate electrode 632. A first p typesemiconductor region 671 is formed in the semiconductor film 606 throughthe above steps.

[0118] The first n type semiconductor regions formed in the n-channelTFTs are LDD (lightly doped drain) regions. When overlapping gateelectrodes, as in the n-channel TFT 653, the LDD regions can ease thehigh electric field region generated in an end of the drain and preventdegradation due to the hot carrier effect. On the other hand, an LDDregion that is placed outside a gate electrode as in the n-channel TFT654 can reduce OFF current.

[0119] The p-channel TFT 652 has a single drain structure. Instead, itmay take a structure in which an offset region is formed between thechannel formation region and the impurity region by adjusting the thirdetching treatment time so as to move an end of the gate electrode andmake space for the offset region. This structure can also be employed bythe n-channel TFT 654, and is very effective in reducing OFF current.

[0120] An element substrate in which a pixel portion and a drivingcircuit are formed on the same substrate from TFTs is obtained in thisway. According to the element substrate manufacturing process of thisembodiment, TFTs having different LDD region structures can be formed onthe same substrate with five photo masks.

[0121] In this manufacture process for TFTs, the heat treatmentapparatus of the present invention can be used to conduct activation, asin Embodiment 3. Activation by the heat treatment method of the presentinvention takes only a short period of time and does not damage asubstrate.

[0122] Embodiment 5

[0123] This embodiment gives a description with reference to FIGS. 8A to8C on an example of a semiconductor film forming method that can beapplied to Embodiment 3 or Embodiment 4. The semiconductor film formingmethod illustrated in FIGS. 8A to 8C includes doping the entire surfaceof an amorphous silicon film with a metal element beforecrystallization. The metal element used is one selected from the groupconsisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au, or acombination thereof. Typically, Ni is employed. It has been found thatthese elements are capable of lowering the heat treatment temperaturefor crystallization and shortening the heat treatment time.

[0124] In FIG. 8A, a glass substrate typical example of which is theCorning #1737 glass substrate (product of Coming Incorporated) is firstprepared as a substrate 551. On a surface of the substrate 551, asilicon oxynitride film is formed by plasma CVD from SiH₄ and N₂O tohave a thickness of 100 nm as a first insulating film 552. The firstinsulating film is provided in order to prevent an alkaline metalcontained in the glass substrate from diffusing into a semiconductorfilm to be formed on the first insulating film.

[0125] An amorphous silicon film 553 is formed by plasma CVD. SiH₄ isintroduced to a reaction chamber and then decomposed by intermittentelectric discharge or pulse electric discharge to be deposited on thesubstrate 551. For example, the film formation conditions includemodulating a high frequency power of 27 MHz and setting the repetitionfrequency to 5 kHz and the duty ratio to 20% for intermittent electricdischarge to deposit SiH₄ to have a thickness of 54 nm. Of course,continuous electric discharge using 13.56 MHz power may be used instead.In order to reduce impurities such as oxygen, nitrogen, and carbon inthe amorphous silicon film 553, SiH₄ used has to have a purity of99.9999% or higher. The plasma CVD apparatus used has a reaction chamberwhich is 13 liter in volume and has a compound molecular pump capable ofexhausting 300 liters per second at a first stage and a dry pump capableof exhausting 40 m³ per hour at a second stage. This structure preventsreverse diffusion of organic vapors from the exhaust system side andraise the attained vacuum in the reaction chamber, whereby a minimumamount of impurity elements are allowed to mix in the amorphoussemiconductor film during its formation.

[0126] Then, a nickel acetate solution containing 10 ppm of nickel byweight is applied using a spinner to form a nickel containing layer 554.To make the solution permeate well, the amorphous silicon film 553 issubjected to surface treatment. The surface treatment includes forming avery thin oxide film from an ozone containing aqueous solution, etchingthe oxide film with a mixture solution of fluorine acid and hydrogenperoxide to form a clean surface, and then treating the surface with theozone containing aqueous solution to form a very thin oxide film again.Since a silicon surface is hydrophobic in nature, the oxide film thusformed helps the nickel acetate solution to be applied uniformly.

[0127] Next, hydrogen is released from the amorphous silicon filmthrough one hour heat treatment at 500° C. Another heat treatment isthen conducted at 580° C. for four hours to crystallize the amorphoussilicon film. Thus formed is a crystalline silicon film 555 shown inFIG. 8B.

[0128] In order to raise the crystallization ratio (the ratio of crystalcomponents to the total volume of the film) and repair defects remainingin crystal grains, the crystalline silicon film 555 is irradiated withlaser light 556 through laser annealing. The laser light used is excimerlaser light having a wavelength of 308 nm and oscillating at 30 Hz. Thelaser light is collected by an optical system into a beam of 100 to 300mJ/cm², and the laser treatment is given with the overlapping ratio setto 90 to 95% while avoiding melting of the semiconductor film. As aresult, a crystalline silicon film 557 is obtained.

[0129] The crystalline silicon film 557 is divided into islands to forma semiconductor film 558. The semiconductor film thus obtained can beadopted by Embodiment 3 and Embodiment 4 without any modification.

[0130] Embodiment 6

[0131] This embodiment describes with reference to FIG. 9 an example ofperforming gettering on the semiconductor film obtained in Embodiment 5to remove the metal element remaining in the film. The gettering methoddescribed here is for removing the metal element from a channelformation region of a TFT through gettering. In FIG. 9, a firstinsulating film 562, a semiconductor film 563, a second insulating film567, a first conductive film 568, and a second conductive film 569 arelayered on a substrate 561. The semiconductor film 563 is the one formedin accordance with the method of Embodiment 5, and has an n typesemiconductor region 565 that contains phosphorus in a concentration of1×10²⁰ to 1×10²¹ atoms/cm³.

[0132] When the semiconductor film 563 is used to form a TFT, the n typesemiconductor region 565 serves as a source or drain region of the TFTwhereas a region 564 serves as a channel formation region of the TFT. Inthe channel formation region, the metal element used in the doping forcrystallization remains in a concentration of 1×10¹⁷ to 1×10¹⁹atoms/cm³. The heat treatment method of the present invention makes theremaining metal element to segregate in the n type semiconductor region565, thus achieving gettering.

[0133] This heat treatment method follows the description of Embodiment1 and the semiconductor film is irradiated with pulsative radiation 570from the substrate side. The pulsative radiation shown as a curve A inthe graph of FIG. 3 is suitable. With the pulsative radiationrepresented by the curve A, the semiconductor film is heated at a rateof 100 to 200° C. per second until it reaches 1100° C., kept at 1100° C.for four seconds, and then cooled down to 300 to 400° C. at a rate of 50to 150° C. per second. One such radiation is enough to obtain thegettering effect. However, it is more desirable to repeat the pulsativeradiation 2 to 10 times. In this way, the concentration of the metalelement used in the crystallization step can be reduced to less than1×10 ¹⁷ atoms/cm³.

[0134] This gettering method can be combined with Embodiment 3 or 4. Forinstance, the gettering described in this embodiment can be combinedwith the heat treatment for activation in Embodiment 4.

[0135] Embodiment 7

[0136] This embodiment describes a process of manufacturing an activematrix-driven liquid crystal display device from a substrate on which adriving circuit and a pixel portion are formed and which is obtained inaccordance with Embodiment 4 (the substrate is called an elementsubstrate). FIG. 14 shows an element substrate 700 bonded to an oppositesubstrate 701 with a sealing member. Columnar spacers 704 and 705 areformed on the element substrate 700. It is appropriate to position thecolumnar spacer 704 at the indention of a contact portion formed on apixel electrode. The height of the columnar spacer 704 is set to 3 to 10μm, though it varies depending on the liquid crystal material used. Thecontact portion has a concave portion corresponding to a contact hole,and disturbance in liquid crystal orientation can be avoided bypositioning the spacer at the concave portion. Thereafter an orientedfilm 706 is formed and subjected to rubbing treatment. A transparentconductive film 702 and an oriented film 703 are formed on one surfaceof the opposite substrate 701. The element substrate 700 is then bondedto the opposite substrate 701 with a seal 707 and a liquid crystal isinjected to form a liquid crystal layer 708. Thus the activematrix-driven liquid crystal display device is completed.

[0137] Embodiment 8

[0138] This embodiment describes with reference to FIG. 15 a processmanufacturing an active matrix-driven light emitting device from TFTsobtained in accordance with Embodiment 4.

[0139] A glass substrate is used for a substrate 1601. On the glasssubstrate 1601, an n-channel TFT 1652 and a p-channel TFT 1653 areformed in a driving circuit portion 1650 whereas a switching TFT 1654and a current controlling TFT 1655 are formed in a pixel portion 1651.These TFTs are composed of semiconductor layers 1603 to 1606, a secondgate insulating film 1607 that serves as a gate insulating film, gateelectrodes 1608 to 1611, and others.

[0140] A first insulating film 1602 formed on the substrate 1601 is asilicon oxynitride (expressed as SiO_(x)N_(y)) film or a silicon nitridefilm with a thickness of 50 to 200 nm. An interlayer insulating filmconsists of an inorganic insulating film 1618 such as a silicon nitridefilm or a silicon oxynitride film and an organic insulating film 1619such as an acrylic film or a polyimide film.

[0141] In the driving circuit portion 1650, a gate signal line sidedriving circuit and a data signal line side driving circuit aredifferent in circuit structure but explanations thereof are omittedhere. Wiring lines 1612 and 1613 are connected to the n-channel TFT 1652and the p-channel TFT 1653, respectively. The TFTs are used to constructcircuits such as a shift register, a latch circuit, and a buffercircuit.

[0142] In the pixel portion 1651, a data wiring line 1614 is connectedto the source side of the switching TFT 1654 whereas a wiring line 1615is connected to the drain side thereof. The wiring line 1615 isconnected to the gate electrode 1611 of the current controlling TFT1655. The source side of the current controlling TFT 1655 is connectedto a power supply wiring line 1617, and a drain side electrode 1616 ofthe TFT 1655 is connected to an anode of an EL element.

[0143] The EL element has the anode, a cathode, and a layer containingan organic compound that provides electroluminescence (hereinafterreferred to as EL layer), with the EL layer interposed between the anodeand the cathode. The EL element is formed on the TFTs of the pixelportion. Luminescence provided by organic compounds are divided intolight emission upon returning from singlet excitation to the base state(fluorescence) and light emission upon returning from triplet excitationto the base state (phosphorescence). Luminescence in the presentinvention includes both.

[0144] The EL element is formed after banks 1620 and 1621 are formedfrom an organic resin such as acrylic and polyimide, preferably, aphoto-sensitive organic resin, so as to cover the wiring lines. In thisembodiment, an EL element 1656 is composed of an anode 1622 formed ofITO (indium tin oxide), an EL layer 1623, and a cathode 1624 formed ofan alkaline metal or an alkaline earth metal such as MgAg and LiF. Thebanks 1620 and 1621 cover ends of the anode 1622 to prevent shortcircuit between the cathode and the anode.

[0145] The cathode 1624 of the EL element is placed on the EL layer1623. The material of the cathode 1624 contains an element having asmall work function, such as magnesium (Mg), lithium (Li), or calcium(Ca). Preferably, an electrode formed of MgAg (obtained by mixing Mg andAg with a ratio of Mg to Ag set to 10:1) is used for the cathode. Otherexamples of the cathode include a MgAgAl electrode, a LiAl electrode,and a LiFAl electrode.

[0146] During the laminate of the EL layer 1623 and the cathode 1624 forone pixel is formed, the laminate for another pixel cannot be formed.However, photolithography that is the usual solution for such case isnot an option here because the EL layer 1623 is extremely weak againstmoisture. In addition, the cathode 1624 formed of an alkaline metal iseasily oxidized. Accordingly, the EL layer and the cathode areselectively formed by a vapor phase method such as vacuum evaporation,sputtering, or plasma CVD using a metal mask or other physical mask. Aprotective electrode may be laid on the cathode 1624 in order to protectthe EL layer from moisture on the outside. The protective electrode ispreferably formed of a low resistant material containing aluminum (Al),copper (Cu), or silver (Ag).

[0147] In order to obtain high luminance with small power consumption,an organic compound that emits light by a triplet exciton (the compoundis hereinafter referred to as triplet compound) is used for the materialof the EL layer. A singlet compound refers to a compound that emitslight through singlet excitation alone whereas a triplet compound refersto a compound that emits light through triplet excitation.

[0148] Materials given as typical triplet compounds are organiccompounds described in the following articles: (1) T. Tsutsui, C.Adachi, S. Saito, Photochemical Processes in Organized MolecularSystems, ed. K. Honda, (Elsevier Sci. Pub., Tokyo, 1991) P. 437. (2) M.A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E.Thompson, S. R. Forrest, Nature 395 (1998) p.151. This paper disclosesorganic compounds given by the following equation. (3) M. A. Baldo, S.Lamansky, P. E. Burrows, M. E. Thompson. S. R. Forrest, Appl. Phys.Lett., 75 (1999) p.4. (4) T. Tsutsui, M. J. Yang, M. Yahiro, K.Nakamura, T. Watanabe, T. Tsuji, Y. Fukuda, T. Wakimoto, S. Mayaguchi,Jpn. Appl. Phys., 38 (12B) (1999) L1502.

[0149] The triplet compounds above have higher light emission efficiencythan singlet compounds and require lower operation voltage (voltagenecessary to cause an EL element to emit light) to emit light of thesame luminance.

[0150] In FIG. 15, the switching TFT 1654 has a multi-gate structure andthe current controlling TFT 1655 has an LDD region that overlaps thegate electrode. A TFT formed of polycrystalline silicon has highoperation speed and therefore is liable to deteriorate upon hot carrierinjection. For that reason, to form TFTs structured differently to suittheir respective functions (the switching TFT having satisfactorily lowOFF current and the current controlling TFT resistant to hot carrierinjection) in one pixel, as shown in FIG. 15, is very effective inmanufacturing a display device that is highly reliable and capable ofexcellent image display (has high operation performance). The activematrix-driven light emitting device is thus completed.

[0151] Embodiment 9

[0152] A crystalline semiconductor film is doped with phosphorus, whichis then activated by the heat treatment method of the present invention.Three samples of this are prepared and their micrographs arerespectively shown in FIGS. 17A to 17C. Each sample has a structuresimilar to the one shown in FIG. 4, and has a glass substrate on which asilicon oxynitride film with a thickness of 100 nm, a semiconductor filmwith a thickness of 50 nm, and a silicon oxynitride film with athickness of 80 nm are layered. A 30 nm thick tantalum nitride film anda 300 nm thick tungsten film that are formed by patterning are furtherplaced thereon.

[0153] As well known, a region doped with an impurity element by iondoping is turned amorphous at the impact of the ions. After that heattreatment is necessary in order to recrystallize the amorphous regionand activate the impurity element at the same time.

[0154] The samples are irradiated with the radiation equivalent to thepulsative radiation represented by the curve A (holding time: 4 seconds)in the graph of FIG. 3 or the pulsative radiation represented by thecurve B (holding time: 0.75 second). FIG. 17A is the picture of thesample that is irradiated once with the pulsative radiation of the curveB. Spots are observed in a region where the semiconductor film isexposed, indicating that the film is not crystallized much. Uponinspecting the photos, a dark part is judged as an amorphous portionwhereas a light part is judged as a crystalline portion based on rule ofthumb. FIG. 17B is the picture of the sample that is irradiated fourtimes with the pulsative radiation of the curve B. Spots are observedhere as in FIG. 17A but they are smaller in number. FIG. 17C is thepicture of the sample that is irradiated once with the pulsativeradiation of the curve A. Most part of the semiconductor film in FIG.17C is crystalline.

[0155] The above results show that the heat treatment method of thepresent invention is capable of activating phosphorus injected by iondoping without damaging the substrate, and that several timesirradiation produces better outcome, though depending on irradiationconditions.

[0156] Embodiment 10

[0157] The various kinds of semiconductor devices can be formed by usingthe present invention. The semiconductor devices, which can be appliedto the present invention, include portable information terminals(electronic notebook, mobile computer, cell phone, etc.), video camera,still camera, personal computer, TV and projector. Their examples areshown in FIGS. 18A to 18E, 19A to 19C and 20A to 20D.

[0158]FIG. 18A shows a cellular phone which comprises a display panel2701, an operation panel 2702 and a connection portion 2703, the displaypanel 2701 including a display device 2704 typified by a liquid crystaldisplay device or an EL display device, a voice output unit 2705 and anantenna 2709. The operation panel 2702 includes operation keys 2706, apower source switch 2707, a voice input unit 2708, and so on. Thisinvention forms the display device 2704 and the cell phone can beaccomplished.

[0159]FIG. 18B shows a video camera which comprises a main body 9101, adisplay device 9102 typified by a liquid crystal display device or an ELdisplay device, a voice input unit 9103, operation switches 9104, abattery 9105 and an image receiving unit 9106. The invention can beapplied to the display device 9102 and the video camera can beaccomplished.

[0160]FIG. 18C shows a mobile computer or a portable informationterminal which is constituted by a main body 9201, a camera unit 9202, apicture unit 9203, operation switches 9204 and a display device 9205typified by a liquid crystal display device or an EL display device. Thesemiconductor device of this invention can be applied to the displaydevice 9205 and the portable information terminal can be accomplished.

[0161]FIG. 18D shows a TV receiver constituted by a main body 9401, aspeaker 9402, a display device 9403 typified by a liquid crystal displaydevice or an EL display device, a receiver unit 9404 and an amplifierunit 9405. The invention can be applied to the display device 9403 andthe TV can be accomplished.

[0162]FIG. 18E shows a portable notebook constituted by a main body9501, display device 9503 typified by a liquid crystal display device oran EL display device, a storage medium 9504, operation switches 9505 andan antenna 9506, which is used for displaying data stored in a mini-disk(MD) or in a DVD and for displaying data received by the antenna. Theinvention can be applied to the display device 9503 and the portablenotebook can be accomplished.

[0163]FIG. 19A shows a personal computer constituted by a main body9601, an image input unit 9602, a display device 9603 typified by aliquid crystal display device or an EL display device and a keyboard9604. The invention can be applied to the display device 9603 and thepersonal computer can be accomplished.

[0164]FIG. 19B shows a player using a recording medium recording aprogram (hereinafter referred to as recording medium), which isconstituted by a main body 9701, a display device 9702 typified by aliquid crystal display device or an EL display device, a speaker unit9703, a recording medium 9704 and operation switches 9705. This deviceuses a DVD (digital versatile disc) or a CD as a recording medium, withwhich the user can enjoy appreciating music, movies, or playing games orInternet. The invention can be applied to the display device 9702 andthe player can be accomplished.

[0165]FIG. 19C shows a digital camera constituted by a main body 9801, adisplay device 9802 typified by a liquid crystal display device or an ELdisplay device, an eyepiece unit 9803, operation switches 9804 and animage receiving unit (not shown). The invention can be applied to thedisplay device 9802 and the digital camera can be accomplished.

[0166]FIG. 20A shows a front-type projector constituted by a projector3601 and a screen 3602. The invention can be applied to the projector3601 and the front-type projector can be accomplished.

[0167]FIG. 20B shows a rear-type projector constituted by a main body3701, a projector 3702, a mirror 3703 and a screen 3704. The inventioncan be applied to the liquid crystal display device integrated to theprojector 3702 and the rear-type projector can be accomplished.

[0168]FIG. 20C is a diagram illustrating an example of structures of theprojectors 3601 and 3702 in FIGS. 20A and 20B. The projectors 3601, 3702are constituted by an optical system 3801 of a source of light, mirrors3802, 3804 to 3806, a dichroic mirror 3803, a prism 3807, a liquidcrystal display device 3808, a phase difference plate 3809 and aprojection optical system 3810. The projection optical system 3810 isconstituted by an optical system inclusive of a projection lens. Thoughthis embodiment shows an example of the three-plate type, there may beemployed the one of the single-plate type without being limited thereto.In the optical paths indicated by arrows in FIG. 20C, further, the usermay suitably provide an optical system such as an optical lens, a filmhaving a polarizing function, a film for adjusting the phase differenceor an IR film.

[0169]FIG. 20D is a diagram illustrating an example of the structure ofthe optical system 3801 of the source of light in FIG. 20C. In thisembodiment, the optical system 3801 of the source of light isconstituted by a reflector 3811, a source of light 3812, lens arrays3813, 3814, a polarizer/converter element 3815 and a focusing lens 3816.The optical system of the source of light shown in FIG. 20D is only anexample, and is not particularly limited thereto only. For example, theuser may suitably provide the optical system of the source of light withan optical system such as an optical lens, a film having a polarizingfunction, a film for adjusting the phase difference or an IR film.

[0170] Though not diagramed, the invention can be further applied as adisplay device to navigation systems as well as to refrigerators,washing machines, microwave ovens, fixed telephones and display deviceintegrated facsimile. Thus, the invention has a very wide range ofapplications and can be applied to a variety of products.

[0171] Embodiment 11

[0172] Described in this embodiment with reference to FIGS. 21A and 21Bis an example of using a reverse stagger TFT to constitute a pixelportion of a liquid crystal display device. FIG. 21A is an enlarged topview of one of pixels in the pixel portion formed on an elementsubstrate. FIG. 21B is a sectional view of the pixel portion taken alongthe dotted line A-A′ of FIG. 21A.

[0173] In FIG. 21B, reference symbol 851 denotes a substrate on which abase insulating film (not shown) is formed first.

[0174] In the pixel portion, a pixel TFT is an n-channel TFT. A gateelectrode 852 is formed on the base insulating film that has been formedon the substrate 851. Formed on the gate electrode 852 are a firstinsulating film 853 a that is a silicon nitride film and a secondinsulating film 853 b that is a silicon oxide film. Second n typeimpurity regions 854 to 856, channel formation regions 857 and 858, andfirst n type impurity regions 859 and 860 are formed as an active layeron the second insulating film. The second impurity regions 854 to 856serve as source regions or drain regions. The first n type impurityregion 859 is placed between the second n type impurity region 854 andthe channel formation region 857. The first n type impurity region 860is placed between the second n type impurity region 855 and the channelformation region 858. The channel formation regions 857 and 858 areprotected by insulating layers 861 and 862, respectively. A firstinterlayer insulating film 863 covers the insulating layers 861 and 862and the active layer. After contact holes are formed in the firstinterlayer insulating film 863, a wiring line 864 connected to thesecond n type impurity region 854 is formed and a pixel electrode 865formed of Al or Ag is connected to the second n type impurity region856. A passivation film 866 is formed thereon. Denoted by 870 is a pixelelectrode adjacent to the pixel electrode 865.

[0175] In this embodiment, gate wiring is made in such a way that thepixel TFT of the pixel portion has a double gate structure. However, thepixel TFT may take a triple gate or other multi-gate structure to reducefluctuation in OFF current. It can also take a single gate structure toimprove the aperture ratio.

[0176] A capacitor in the pixel portion is composed of a capacitancewiring line 871 and the second n type impurity region 856, with thefirst insulating film and the second insulating film as dielectric.

[0177] Needless to say, the pixel portion shown in FIGS. 21A and 21B ismerely an example and it is not limited to the above structure.

[0178] The heat treatment apparatus of the present invention can be usedto carry out heat treatment in manufacturing the pixel portion TFT shownin FIG. 21B. For example, the apparatus can be used for activation andgettering of an impurity element contained in the second n type impurityregions. The apparatus is the one described in Embodiment 1 or 2, andirradiates the regions several times through pulsative radiation. Theregions may be irradiated with the pulsative radiation from thesubstrate side or the opposite side thereof.

[0179] A liquid crystal display device is obtained from the elementsubstrate of this embodiment when following the description inEmbodiment 7. The liquid crystal display device thus manufactured can beused as a display unit of various electronic equipments shown inEmbodiment 10.

[0180] Embodiment 12

[0181] This embodiment gives descriptions on characteristics of a TFTformed from a semiconductor film on which gettering treatment shown inEmbodiment 6 is performed. The TFT has the single drain structure andthe channel length thereof is 10 μm whereas the channel width is 8 μm.The catalytic element reducing effect of gettering is evaluated with theOFF current value as a substitute characteristic. If the OFF currentvalue is 1 pA or lower, the effect of gettering is consideredsatisfiable.

[0182] In the gettering, the highest temperature is set to 690 to 730°C. and the holding time is set to 300 seconds. Irradiation is repeatedthree times under these conditions.

[0183]FIG. 22 is an ogive graph showing the OFF current valuedistribution (fluctuation) for 94 samples. The graph also shows, forcomparison, data of samples subjected to gettering treatment at 550° C.for four hours in a furnace annealing. According to the graph, there isno significant difference between the two groups. The graph shows thatthe heat treatment method of the present invention provides excellentgettering in a shorter time than the conventional gettering using afurnace annealing takes.

[0184] The heat treatment method of the present invention makes itpossible to conduct activation and gettering of an impurity element usedto dope a semiconductor film in a short period of time without damaginga substrate. The heat treatment apparatus of the present invention makessuch heat treatment possible. The productivity in manufacturing asemiconductor device can be improved by employing this heat treatmentmethod.

What is claimed is:
 1. A heat treatment method comprising the step of:heating a treatment object by irradiating it through radiation from alamp light source, wherein the radiation from said lamp light sourcelasts 0.1 to 20 seconds at a time, wherein the radiation from said lamplight source is repeated several times.
 2. A heat treatment methodcomprising the step of: heating a treatment object by irradiating itthrough radiation from a lamp light source, wherein the radiation fromsaid lamp light source is pulsatively repeated several times such thatthe treatment object holds the temperature to its highest for 0.5 to 5seconds.
 3. A heat treatment method comprising the steps of: holding atreatment object in a processing chamber filled with a coolant; andheating the treatment object by irradiating it through radiation from alamp light source, wherein the radiation from said lamp light source isheld for 0.1 to 20 seconds at a time, wherein the radiation from saidlamp light source is repeated several times.
 4. A heat treatment methodcomprising the steps of: holding a treatment object in a processingchamber filled with a coolant; and heating the treatment object byirradiating it through radiation from a lamp light source, wherein theradiation from said lamp light source is repeated several times suchthat the treatment object holds the temperature to its highest for 0.5to 5 seconds.
 5. A heat treatment method comprising the steps of:holding a treatment object in a processing chamber filled with acoolant; and heating the treatment object by irradiating it throughradiation from a lamp light source, wherein said lamp light source isturned on and the radiation from said lamp light source is held for 0.1to 20 seconds at a time, while an amount of supply of the coolant isreduced, wherein said lamp light source is turned off while a treatmentof increasing the amount of supply of the coolant as one cycle isrepeated several times.
 6. A heat treatment method comprising the stepsof: holding a treatment object in a processing chamber filled with acoolant; and heating the treatment object by irradiating it thoughradiation from a lamp light source, wherein said lamp light source isturned on while an amount of supply of the coolant is reduced, whereinsaid lamp light source is turned off while a treatment of increasing theamount of supply of the coolant as one cycle is repeated several times,after the treatment object holds the temperature to its highest for 0.5to 5 seconds.
 7. A heat treatment method according to claim 1, whereinsaid lamp light source is selected from the group consisting of ahalogen lamp, a metal halide lamp, a xenon lamp, a high pressure mercurylamp, a high pressure sodium lamp and an excimer lamp.
 8. A heattreatment method according to claim 2, wherein said lamp light source isselected from the group consisting of a halogen lamp, a metal halidelamp, a xenon lamp, a high pressure mercury lamp, a high pressure sodiumlamp and an excimer lamp.
 9. A heat treatment method according to claim3, wherein said lamp light source is selected from the group consistingof a halogen lamp, a metal halide lamp, a xenon lamp, a high pressuremercury lamp, a high pressure sodium lamp and an excimer lamp.
 10. Aheat treatment method according to claim 4, wherein said lamp lightsource is selected from the group consisting of a halogen lamp, a metalhalide lamp, a xenon lamp, a high pressure mercury lamp, a high pressuresodium lamp and an excimer lamp.
 11. A heat treatment method accordingto claim 5, wherein said lamp light source is selected from the groupconsisting of a halogen lamp, a metal halide lamp, a xenon lamp, a highpressure mercury lamp, a high pressure sodium lamp and an excimer lamp.12. A heat treatment method according to claim 6, wherein said lamplight source is selected from the group consisting of a halogen lamp, ametal halide lamp, a xenon lamp, a high pressure mercury lamp, a highpressure sodium lamp and an excimer lamp.